Thermally curing aryl-ethynyl end-capped imide oligomers: Study of new aromatic end caps

Two new aryl - ethynyl end-cap model compounds, N-phenyl-4-(1-naphthylethyn yl)phthalimide (I) and N-phenyl-4-(2-naphthylethynyl)phthalimide (8), were synthesized and characterized. The single-crystal molecular structure of 1 reveals an alternating "head to tail" packing mode whereas the "heads and t ails" of 2 are aligned and not alternating. The thermal cure kinetics of 1 and 3 were analyzed using NMR and FT-IR spectroscopy, respectively and comp ared to N-phenyl-4-phenylethynylphthalimide (2). In both cases the naphthyl -ethynyl model compounds reacted faster than the phenyl-ethynyl derivative. The end-capped imide oligomers analogues of 1 and 2, NETI-5 and PETI-5, re spectively, were synthesized and their thermal cure kinetics were analyzed by DSC. The thermal cure kinetics of I and 2 best fit a first-order rate la w. Compound I cures at faster rates than 2, although the calculated E-a, va lues of 1 and 2 are statistically indistinguishable. The thermal cure kinet ics of 2 and 3 also fit a first-order rate law and show that the E-a, of 3 is higher than that of 2, although 3 thermally cures at slightly faster rat es than 2, but slower than 1 (H-1 NMR) at the temperatures studied. The E-a , values determined for 2 by H-1 NMR and by FT-IR differ significantly. The DSC thermal cure kinetics of NETI-5 and PETI-5 best fit a first-order rate law and revealed a rate acceleration trend similar to that observed for th e model compounds 1 and 2. Effectively, NETI-5 cures at the same rate as PE TI-5 but at approximately a 30 degreesC lower curing temperature.